Many had been stranded on open land for several days amid government fears that IS might have infiltrated them.

Image copyrightReutersImage caption
Many of the displaced were not allowed to cross the River Euphrates until Wednesday

Residents still left in Ramadi told the Associated Press news agency that IS fighters were urging them over loudspeakers not to be afraid and to stay in the city.

According to Anbar provincial officials, at least 500 people were killed in three days of fighting in Ramadi last week.

'Devastating car bombs'

Col Ryder described the waves of "vehicle-borne improvised explosive devices" (VBIEDs) used by IS in their offensive as "devastating".

"These enormous suicide VBIEDs is something that we have to help the Iraqis, and our partners in Syria, defeat," he said.

Iraqi troops in the area are expected to launch an attack on IS soon and they could be joined by about 3,000 Shia militia fighters.

But the BBC's Gary O'Donoghue in Washington says the US insists it will only provide air cover to fighters under the control of the Iraqi government - reflecting concerns that some of the groups are controlled by Iran.